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Notes from the Field: Salmonella Typhi Infections Associated with Contaminated Water — Zimbabwe, October 2011–May 2012

On October 25, 2011, a cluster of approximately 20 suspected cases of typhoid fever in residents of Dzivaresekwa, a high-density suburb of Harare, Zimbabwe, was reported to the City of Harare City Health Department. On November 22, a team from CDC-Atlanta, CDC-Kenya/Kenya Medical Research Institute, and the South Africa Field Epidemiology and Laboratory Training Program, was invited to assist with the investigation by providing epidemiologic and microbiologic support to better describe the outbreak and to evaluate response efforts.

As of May 2, 2012, a total of 4,185 suspected cases of typhoid fever had been identified in Harare. Suspected cases were defined as fever of ≥3 days duration and malaise, headache, vomiting, diarrhea, constipation, or cough in a person who lived in or had been in Harare since October 1, 2011. Confirmed cases (n = 52) met the suspected case definition and were confirmed by blood or stool culture. Median age of patients was 15 years (range: <1–95 years); 54% were female. Hospitalization was reported for 1,788 patients (43%); two deaths were reported. Suspected cases were reported predominantly in the high-density suburbs of Kuwadzana (1,957), Dzivaresekwa (1,012), and Marlborough (115). Of patients treated in Harare, 207 reported home addresses in other Zimbabwean provinces. Suspected cases of typhoid fever in Harare continue to decline as of May 2, 2012; however, with limited surveillance systems and laboratory capacity, national trends are unclear.

The investigative team, in collaboration with government officials, tested water samples from six public boreholes, seven shallow wells, and three municipal taps in Dzivaresekwa. Samples from two of six boreholes and all seven shallow wells yielded Escherichia coli (an indicator of fecal contamination); all municipal taps tested negative for E. coli.

Recommendations included promotion of household chlorination of water from all sources because chlorination of the municipal system might be unreliable. Public health partners targeted distribution of a 3-month supply of sodium dichloroisocyanurate water-purification tablets (i.e., enough tablets to treat a single 20-liter bucket for drinking water every day per household for 3 months) to all households in suburbs that were defined as being at high risk, and disseminated health education messages highlighting the importance of safe water collection, treatment, and storage, safe food preparation, and improved hygiene and sanitation practices. Efforts are under way to upgrade infrastructure (replacing old cast-iron pipes with new polyvinyl chloride pipes to prevent breakages), remediate existing boreholes by shock chlorination and drilling new ones, and establish local reservoir tanks.

Although this descriptive study does not prove that illness was associated with contaminated water, the association seems likely. Rural-to-urban migration has resulted in overcrowding in residential areas and has outpaced maintenance and expansion of water supply and sewerage infrastructure. Rationing of piped, treated water from municipal systems obliges residents to use unimproved water sources to meet their water needs, putting them at risk for enteric infections. Frequent sewer blockages compound this problem by further contaminating shallow wells used by residents for drinking water.

Each year, Salmonella Typhi causes an estimated 22 million cases of typhoid fever and 216,000 deaths worldwide (1). Humans are the only reservoir for S. Typhi, and infection occurs by the fecal-oral route, usually through ingestion of contaminated food or water. An estimated 884 million persons worldwide lack access to safe water, and nearly 2.5 billion persons do not have access to adequate sanitation (2). Incidence is highest in developing countries, particularly in areas with poor sanitation or without access to safe water. Recent evidence of the magnitude of epidemic and endemic typhoid fever in sub-Saharan African countries highlights the continued importance of typhoid fever prevention and control in Africa (3).

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